Frost Dates for 20877 — Gaithersburg, Maryland

Half of springs at Rockville 1 NE, MD see their last 32°F night by April 1; only one in ten is past it by March 19, and one in ten still has one after April 15. Planting tender crops after April 6 leaves a 30% risk of a frost on them, after April 10 20%, and after April 15 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 62% of the 50 Maryland stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 6 in half of years, as early as October 24 one year in ten, and holds off past November 21 one year in ten. A hard freeze of 28°F follows 13 days later, around November 19; in spring the one-in-ten date for 28°F is April 4, 11 days before the 32°F one. The freeze-free season lasts 219 days in a typical year, longer than at 76% of the 50 Maryland stations; it reaches 240 days one year in ten and falls short of 200 one year in ten. On average 86 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 15 days longer, to about April 16, and return around October 25. Severe cold of 16°F or below comes in 97% of winters, usually between January 2 and February 15.

July is the warmest month at Rockville 1 NE, MD, averaging 87°F by day and 69°F at night; January is the coldest at 42°F and 27°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 52% of years.

Warmth for growing adds up to 3,981 growing degree days a year (base 50°F), more than at 60% of the 50 Maryland stations. 36% of them (1,425) have built up by the end of June, and July adds the most, 866. Precipitation totals 41.5 inches a year, most in June (4.0") and least in February (2.6"); May to September bring 45% of it.

The nearest other station, Damascus 3 SSW, MD, 9 miles north of Gaithersburg and 260 feet higher, has a last frost 13 days later (April 14), a first frost 8 days earlier (October 29), a season 23 days shorter.

The first measurable snow (0.1 inch or more) in Gaithersburg usually arrives around December 27, and the last of the season around March 9. Those are the middle dates across the winters of 1991–2020 at Rockville 1 NE, MD, 3.3 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 23 days after the last snow.

ZIP 20877 is 3 miles from Rockville 1 NE, MD, which stands at 440 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 14 other ZIP codes share the station; its figures are presented in full for 20906 (Silver Spring). The 2023 USDA Plant Hardiness Zone Map lists ZIP 20877 in zone 7b, the band where the coldest night of the year averaged 5 to 10°F (-15.0 to -12.2°C) over 1991–2020; a zone describes winter lows, not frost dates.